Animal feedstuffs are supplemented with individual amino acids according to the requirement of the animals. For supplementing animal feedstuffs, e.g. with L-lysine, L-lysine monohydrochloride having an L-lysine content of 78% is predominantly employed to date. Since L-lysine is prepared by fermentation, for the preparation of the monohydrochloride it must once initially be separated off from all the other constituents of the crude fermentation broth in expensive process steps and then converted into the monohydrochloride, and the latter must be crystallized. A large number of by-products and the reagents needed for the working up are produced as waste by this procedure. Since a high purity of the animal feedstuff supplement is not always necessary and furthermore the by-products of the fermentation often still comprise nutritionally active valuable substances, there has therefore been no lack of attempts in the past to convert L-lysine together with constituents of the fermentation broth into a solid animal feedstuff less expensively.
The complex composition of such media has proved to be a serious disadvantage in the processing. These generally can be dried only with difficulty, and the dried products are often hygroscopic, practically not free-flowing, at risk from the formation of lumps and unsuitable for the industrially demanding processing in mixed feedstuff plants. The products from the fermentation for the preparation of lysine are to be mentioned above all here. Simple dewatering of the crude fermentation broth by spray drying leads to a dusty, highly hygroscopic concentrate which is lumpy after a short storage time and cannot be employed as an animal feedstuff in this form.
The use of a spray dryer with an integrated fluidized bed gives finely divided and porous but free-flowing spray particles with a very low bulk density and a still high hygroscopic nature. A considerable dust nuisance arises in the handling of this product.
Build-up granulation in a fluidized bed has also proved to be not very suitable, since here also large amounts of additional substances (as a rule more than 10 wt.%) are necessary, these being added continuously according to DD 268 856. The use thereof in this context is essential in particular in order to bind the water from the fermentation broth and in this way to prevent the granules from forming lumps, which would have an adverse effect in the case of build-up granulation in particular.
Further processes for the granulation of animal feedstuff additives comprising amino acids and based on fermentation broth are known from U.S. Pat. No. 4,777,051, EP 0 615 693 B and EP 0 533 039 B.
U.S. Pat. No. 4,777,051 discloses a spray drying process with a subsequent additional drying step. Solutions of tryptophan or threonine of varying origin having a content of 20-60 wt. %, based on the total solids content, are sprayed in a first step to give semi-dry granules having a residual moisture content of 5-15%. The moist granules are then spread out on a conveyor belt dryer with a perforated base and finally dried with hot air, a product having a residual moisture content of about 4 wt. % being obtained.
Drying is accordingly carried out in an expensive manner in two stages in two different apparatuses.
According to EP 0 615 693, the granulation is also carried out in a two-stage drying process.
The fermentation broth is spray dried, optionally after removal of some of the constituents, to give fine particles which have a maximum particle size of 100 μm to the extent of min. 70 wt. %, and the fine particles obtained in this way are built up in a second stage to give granules which comprises fine particles to the extent of min. 30 wt. %.
In addition to the two-stage nature of the drying granulation process, the disadvantage of this process is that the granulation can be carried out only batchwise and not continuously.
EP 0 809 940 B1 also discloses a process for the granulation of an animal feedstuff additive based on fermentation broth. The process is characterized in that the fermentation broth is granulated, compacted and dried in a fluidized bed in one step, while an amount of energy sufficient to establish a desired particle diameter and a desired bulk density is introduced into the fluidized bed by a mechanical route, in addition to the energy required for generation of the stationary fluidized bed.
An essential feature of fluidized bed spray granulation is the formation of a stable fluidized bed within the granulator. This means that the speed of the inflow medium must be chosen such that fluidization of the particles to be dried occurs, but pneumatic conveying is avoided. It is thus ensured that the particles formed indeed are not discharged, but a constant change in place of the particles takes place, so that there is a uniform probability of impingement for the drops sprayed in.
This process has the known disadvantages of fluidized bed spray granulation. These are chiefly:
As the particle size decreases, the speed of the inflow medium must be greatly reduced, so that a stable stationary fluidized bed is maintained and discharge of the particles from the granulator is avoided. Since in this process the inflow medium is the energy carrier, the efficiency decreases to an extreme degree. The build-up rates which can be achieved are too low for the granulation process still to be able to be operated economically.
A process of this type is described in U.S. Pat. No. 4,946,654. A loss of material due to the discharge of dust is avoided by separating this off from the gas flowing out of the granulator and recycling it into the fluidized bed.
The lines have dimensions such that only small amounts of solid can be fed back.